In a vehicle, for example, an electrical junction box may be provided in an electric circuit that connects a power supply and a load, the electrical junction box including: a circuit substrate on which a switching element and a control element are mounted; and a housing member that houses the circuit substrate (see JP 2016-158373A).
The switching element connects and disconnects the connection between the power supply and the load. The control element performs control so as to turn the switching element on and off. When the switching element is on, an electric current flows from the power supply to the load through the switching element. When the switching element is off, an electric current does not flow through the switching element, and thus the connection between the power supply and the load is disconnected.
The switching element generates heat when energized. In particular, when an overcurrent flows through the switching element, the switching element overheats. The overheated switching element may catch fire.
However, a fusible link is provided on a conductor wire that connects the power supply or the load to the switching element. When an overcurrent flows through the conductor wire, the fusible link blows out. As a result, the overcurrent is prevented from flowing into the switching element, and thus the switching element is protected from overheating.
Also, when, for example, an electric current that exceeds an upper limit value that is smaller than the overcurrent flows through the switching element, or the temperature of the switching element exceeds an upper limit temperature that is lower than the overheating temperature, the control element turns off the switching element. As a result, the switching element is protected from overheating.
The inventors of the present disclosure assumed an accidental situation in which, for example, the fusible link does not blow out, and the control element does not perform overheat protection of the switching element due to a malfunction of the control element. In such an accidental situation, the switching element overheats and catches fire. Accordingly, a technical problem to be solved is to take measures to cope with an accidental situation.
Thus, it is an object of the present disclosure to provide an electrical junction box in which it is possible to prevent a switching element from catching fire.